The number one thing that has made me a better healer is knowing when to have my holy power loaded up for burst healing, and being more generous with my EF, even if it's a 1pt EF.
Statwise, I think it's up to your own playstyle. I have always favored haste over mastery, though at this gear level, I've moved more towards Mastery > Haste. Keeping an eye on haste breakpoints is a great way to figure out if you really need that extra haste or not. Probably will reforge out of some haste when I get home tonight.
Try to figure out a gameplan for each fight, decide on when you want to use your throughput and raid CDs ahead of time. It helps to have an idea of when to expect damage and be ready for it with all that HP and CDs. Good luck!
p.s. Disc will trounce every healer right now. They're getting nerfed so expect your HPS to go up in 5.2. At the end of the day, as long as the boss dies and your raiders don't, it's a win. I have never been the type of healer (only healing since DS) to try to pad the meters. I heal when I need to and those dang disc priests keep absorbing all the damage :)